The oscillation frequency of a quartz oscillator-plate shifts abruptly when the plate is suddenly exposed to infrared radiation. The shift is downward for BT cut plates and upward for AT plates. That the effect is distinct from normal temperature drift is shown by the fact that it can be made opposite to the normal drift by proper orientation and dimensioning of the plate. The magnitude of the effect is about one part in one hundred thousand, for radiation intensities employed. Since the shift occurs only when the surface of the plate is differentially exposed, it is tentatively concluded that the cause is related to thermal strain.